1. Field of the Invention:
The present invention relates to a method and an apparatus for inspecting the appearance of articles, particularly a method and an apparatus for measuring and inspecting the form, size and surface conditions (such as color, damage, surface ruggedness, etc.) of articles, for example, ball like fruits, vegetables or the like, by photographing the articles by means of a sensor camera and processing their pictures so as to sort them by classifying and grading.
2. Description of the Related Art:
Conventionally, the following apparatuses have been provided which inspect the form, size and surface conditions of fruits, vegetables or the like by using a sensor camera or sensor cameras:
(a) Apparatuses using the inspecting method wherein a sensor camera placed above or at one side of a conveyor photographs the one sided surface of each fruit, vegetable or the like being conveyed (cf. Japanese laid open patent application Sho 55-18285);
(b) Apparatuses using the inspecting method wherein two sensor cameras placed at opposite sides of a conveyor photograph the two sided surfaces of each article being conveyed (cf. Japanese laid open patent application Sho 59-87081);
(c) Apparatuses using the inspecting method wherein four sensor cameras placed at both sides of a conveyor photograph the four sided surfaces of each article such as fruit or vegetable dropped from the other conveyor onto that conveyor (cf. U.S. Pat. No. 4,324,335); and
(d) Apparatuses using the inspecting method wherein a sensor camera placed above a roller conveyor photographs the peripheral part of each article such as fruit or vegetable being conveyed while rotating at a high speed in the conveying direction (cf. U.S. Pat. No. 4,122,951).
To sort round, oval or ball like articles or objects such as fruits or vegetables (hereinafter referred to as "articles") by classifying and grading according to the form, size and surface conditions (such as color, damage, etc.), it is very important to inspect the parts of each article representing the form and size thereof as well as the peripheral surface of the article.
However, the conventional techniques as described above cannot satisfy these requirements.
The method (a) cannot sort articles correctly, because it can inspect only the top or one-sided surface of each article, that is, the limited surface of the article, leaving a large part of its overall surface not inspected.
The method (b) can inspect both sides of the article, that is, a larger part of its overall surface than the method (a). However, the method (b) cannot sort articles correctly, because large parts of their surfaces are left not inspected. Especially, an article like a lemon which presents different forms and sizes of its images according to its orientation cannot be correctly measured and inspected, because it presents different images in size between when its axis is placed in the crosswise direction of the conveyor and when it is in the longitudinal direction of the conveyor. Therefore, it is required to align all articles of this type in the same orientation on the conveyor.
However, it is very difficult to align all articles automatically in the same orientation on the conveyor.
The method (c) can inspect all four sides of an article, that is, a larger part of its surface than the method (b). However, this method presents the disadvantages that the upper and lower parts of the article surface in the dropping direction cannot be inspected and that the part of the article representing the size of the article cannot be measured in form and size, because the orientation of the article cannot be effectively controlled.
The method (d) presents the disadvantages that although it can inspect the peripheral or side surface of an article like a lemon which can be rotated around its core axis in a high circumferential speed, the end parts of the article in the axial direction are left not inspected, that it tends to swing and jump the article in the unstable position during the conveying by rollers so that it is not practically applicable to such articles, and that a small article may be rotated by a turn or more in the same photographing period so that a part of its surface is repeatedly inspected, while a big article may be rotated by less than a turn in the same photographing time so that a part of its surface is left not inspected.
Since objects having different circumferences cannot be rotated by a turn at the same time on the same roller conveyor, the rate of circumferential rotation, which is dependent upon the circumference of the article, makes the inspected areas of articles different from each other.
The methods (c) and (d) which can inspect a larger area of an article than the methods (a) and (b) present the disadvantage that they tend to deteriorate the commercial value (marketability) of articles by giving damages such as bruises or scratches during the dropping or the hig-speed rotation of articles.
In addition, the methods (c) and (d) cannot measure in form and size the part of an article representing the size of the article, because the articles cannot be kept in the same orientation.
The methods which use a plurality of sensor cameras such as the method (c) are complicated and expensive.
To measure and inspect the whole surface of a ball like article, it is preferable that at least the front and rear parts, right and left parts, and upper and lower parts of an article are inspected.
To inspect the six parts of an article, the article may be suspended, or transported on a transparent conveyor. However, the suspension presents the same disadvantages as the method (c), and is not practically applicable. A transparent conveyor may be opaquely stained in its transparent parts during the transportation of articles so that it is not applicable to an inspecting apparatus for many articles.
Articles such as fruits and vegetables tend to receive more damages such as bruises and scratches on their surfaces, in proportion to the number of processes of dropping or rotation to which they are subjected. Therefore, it has been an object of the art to develop a method and apparatus which can inspect a larger surface part of each article without dropping or rotating articles.